This invention relates to compression release engine brakes or retarders, and more particularly to the push rods used with the hydraulic pistons in such apparatus.
Engine brakes or retarders of the compression release type are well known as shown, for example, by Jakuba et al U.S. Pat. No. 4,473,047. In such engine retarders one or more exhaust valves in one or more cylinders of the associated internal combustion engine are opened near top dead center of the compression stroke of the cylinder when the retarder is in operation and the fuel supply to the engine is accordingly cut off. This allows the air compressed during the compression stroke of the cylinder to escape before at least a major portion of the work of compression is recovered during the subsequent power stroke of that cylinder.
In the typical compression release engine retarder the force required to open the exhaust valves as described above is typically derived from another part of the associated engine such as an intake valve push rod, rocker arm, or fuel injector push rod of another cylinder. This mechanical input is picked up by a master piston in a hydraulic circuit in the engine retarder and transmitted to a slave piston via that circuit. The resulting motion of the slave piston is used to open the exhaust valve of the cylinder which is nearing top dead center of its compression stroke. A push rod is typically used to couple the motion of the input element to the master piston, and another push rod is used to couple the motion of the slave piston to the exhaust valve or valves to be opened.
In many engines the mechanical input and/or output elements are rocker arms contacted by one end of the above-mentioned master and/or slave piston push rods. Because the end of such a push rod which is in contact with the rocker arm is moving along a circular arc, while the other end (in contact with the master or slave piston) is constrained to reciprocate linearly with the master or slave piston, both ends of the push rod must slide in associated sockets in order to accommodate the different types of motion experienced by the ends. To minimize wear on such surfaces which are in sliding contact with one another, it is generally necessary for the mating surfaces to be ground and polished. Good lubrication of such surfaces is also helpful to reduce wear. At the master or slave piston end of such push rods, however, the push rod may be deeply recessed in the piston. It is therefore difficult and/or costly to grind and polish the master or slave piston surface which is in contact with the push rod. The recessed nature of this surface also makes it difficult to lubricate it.
In view of the foregoing, it is an object of this invention to improve and simplify push rods and the associated elements of compression release engine retarders.
It is a more particular object of this invention to reduce or eliminate the need for grinding and polishing, as well as the need for lubrication, of the surfaces on at least one end of push rods in compression release engine retarders.